1. Field of the Invention
This invention relates to a vehicle automatic transmission control system, more particularly to a vehicle automatic transmission control system of the type in which the driving resistance is calculated and used as a parameter for determining control values, and still more particularly to such a vehicle automatic transmission control system which enables the driving resistance to be calculated with high precision.
2. Description of the Prior Art
The conventional electronic vehicle automatic transmission control system is generally equipped with a memory device storing a two dimensional shift diagram as a map, hereinafter referred to as "shift diagram map" and the gear ratio is determined by retrieval from the map using the throttle opening and the vehicle speed as address data. Since the shift diagram map is prepared assuming only general driving conditions, however, it does not always enable the selection of an appropriate gear ratio during hill-climbing and other special driving conditions. A number of systems have been developed for overcoming this problem. For example, Japanese Laid-open Patent Publication No. 1(1989)-112059 teaches a system which calculates the driving resistance and uses the result for correcting the map-retrieved gear ratio, while Japanese Laid-open Patent Publication No. 63(1988)-246546 discloses a system which determines the gear ratio through fuzzy reasoning based on operating parameters including the driving resistance, without using the shift diagram map. The assignee also provided control systems of the latter type in Japanese Laid-open Patent Publications No. 2(1990)-3739 and No. 2(1990)-85563 (also filed in the United States to mature as U.S. Pat. No. 5,036,730 and filed in EPO under 89306192.9); No. 2(1990)-3738 (also filed in the United States to mature as U.S. Pat. No. 5,079,705 and filed in EPO under 89306167.1); No. 2(1990)-138,558 and No. 2(1990)-138,561 (also filed in the United States to mature as U.S. Pat. No. 5,067,374 and filed in EPO under 89311976.8); No. 2(1992)-138,559, No. 2(1992)-138,560 and No. 2(1990)-150,558 (also filed in the United States to mature as U.S. Pat. No. 5,079,704 and filed in EPO under 89311970.1); and No. 4(1992)-8964 (also filed in the United States under 691,066 and filed in EPO under 91303878.2).
While it is well known that the driving resistance is the sum of such individual resistances as the rolling resistance, the aerodynamic drag and the like, precise measurement of the driving resistance of a vehicle is possible only under strictly controlled indoor test conditions and is very difficult under actual driving conditions. The aforementioned Japanese Patent Publication No. 63(1988)-246546 therefore uses a driving resistance value obtained by simulation. However, such a simulation value only roughly approximates the actual driving resistance and cannot be considered to reflect it with a very high degree of accuracy. It was in the light of this situation that the assignee proposed the method of computing driving resistance disclosed in the aforesaid Japanese Patent Publication No. 4(1992)-8,964 (U.S. Ser. No. 691,066).